Field
This disclosure relates to a transparent conductor and a touch panel including the conductor.
Description of the Related Art
Transparent conductors, which have transparency and electric conductivity, have been used as transparent electrodes for displays such as liquid crystal displays (LCDs), plasma display panels (PDPs), and electroluminescence (organic EL and inorganic EL) panels and for solar cells, for example. In addition, the transparent conductors have been also used for electromagnetic wave shielding films and infrared ray shielding films, for example.
The transparent conductor is exemplified by ITO prepared by adding tin (Sn) to indium oxide (In2O3), GZO prepared by adding gallium (Ga) to zinc oxide (ZnO), and materials prepared by adding antimony (Sb) to tin oxide (SnO2). Among them, ITO has been widely used.
In recent years, terminals including a touch panel, such as smartphones and tablet terminals have rapidly become popular. In such a terminal, a touch sensor is provided on a liquid crystal panel, and a cover glass is disposed on the outermost face. The touch sensor includes one or two glass or film substrates that are bonded together. On one or both sides of the substrate, an ITO film is formed by sputtering.
The transparent conductor for touch panels is required to have higher visible light transmittance than those for other applications. The sensitivity of human eyes to light varies with a wavelength of the light, and reaches the maximum at a wavelength of 555 nm. Thus, the transparent conductor for touch panels is required to have a high transmittance at a wavelength of 555 nm.
As smartphones, tablet terminals, and PCs with a touch sensor have become popular, touch panels are rapidly becoming larger. The large touch panels are required to have lower resistance while maintaining high transmittance. In addition, the larger touch panels have lager weights, and thus weight reduction by replacing a glass substrate on which the transparent conductor is provided with a film substrate has been studied.
To achieve an ITO film having a lower resistance, the ITO film is required to have a larger thickness or to be thermally annealed for crystallization. An ITO film having a larger thickness unfortunately has a lower transmittance. In addition, film substrates are difficult to be thermally annealed at a high temperature. On this account, the ITO film provided on a film substrate is difficult to have lower resistance while maintaining high transmittance.
In such circumstances, a multilayer transparent conductor having a multilayer structure of a metal oxide layer and a metal layer has been developed. In recent years, the exhaustion of the resource of indium (In), which is a rare earth element, has been a concern, and thus there is a demand for a transparent conductor including no In but satisfying various characteristics. As the material for such a transparent conductor, zinc oxide (ZnO) has been studied.
For example, Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 9-291355) discloses a laminate in which a transparent oxide (GZO) layer prepared by adding Ga to ZnO, a layer of a metal such as silver (Ag), and a GZO transparent oxide layer are stacked. Patent Document 2 (Japanese Patent Application Laid-Open Publication No. 2007-250430) discloses a laminate including a Zn—Sn—O oxide film, a film prepared by adding Ga or Al to the Zn—Sn—O oxide, and a metal film mainly containing Ag.